This invention is directed at a unitary framed filter where the filters form is capable of being formed by a continuous extrusion process.
Conventionally three dimensional filter frames are formed by injection molding or similar type processes. In its simplest variation, the frame is directly formed as a unitary structure. A simple technique for this is described in U.S. Pat. No. 2,032,262 where a pleated filter is held in a jig with only the edge portions extending out of the jig. This jig is then inserted into a mold form and a plastic type material is injected, embedding the exposed pleat edges in the space between the jig and the mold form. Similarly, U.S. Pat. No. 5,792,229 shows an elastomeric filter frame formed directly on a pleated filter media by injection molding a foaming resin into the pleats of the pleated filter along the periphery of the pleated filter in one embodiment of the invention described. This filter requires a separate rigid frame in which the filter is fit into the frame by a friction type fit. A preformed molded frame is described in U.S. Pat. No. 3,296,781. The filter media is subsequently attached to the molded frame by use of an adhesive or the like.
Three-dimensional filter frames can also be formed from multiple pieces, which are then assembled by use of adhesive, welding, friction fit, snap fits, mechanical fasteners or the like. This type of approach permits more flexibility in terms of frame forms and functionality than unitary filter frames, however, it generally results in framed filters which are complicated to manufacture. For example, U.S. Pat. No. 4,692,177 describes a two-piece snap fit filter frame where both of the two pieces are three-dimensional injection molded frame pieces. Fluid bypass is prevented in this particular arrangement by placing a bead of adhesive into a groove in one of the frame pieces and subsequently forcing a top edge of the pleated filter into the adhesive bead during the snap fit assembly process. This type of framed filter would be very difficult to implement in an automated production process due to the strategic placement of the adhesive within an enclosed space and the need for rapid assembly of three three-dimension pieces coming together simultaneously with very close tolerances. A similar approach is described in U.S. Pat. No. 1,832,281, however, the filter media in this embodiment is friction gripped along the periphery of the filter media by mating flanges of the two frame elements, one of which comprises an exhaust flue. U.S. Pat. No. 2,058,669 describes a three-dimensional filter frame formed by cutting out the face portions of two corrugated boxes halves, which halves are subsequently cemented together with a pleated filter and comb-like pleat stabilizing elements. A similar approach is also discussed in U.S. Pat. No. 3,513,643 where the rectangular frame is described as a conventional multi-piece aluminum frame with the frame elements welded together and the filter adhesively attached to the frame. U.S. Pat. No. 4,386,948 describes a filter for use in a respiratory device where the filter frame is a three-piece molded structure where the individual filter frame pieces and filter media are all formed of polypropylene and welded together. The filter media is held between two flanges of two injection molded polypropylene pieces with ultrasonic fusing of the three elements forming a fluid tight seal. U.S. Pat. No. 5,599,446 describes an injection molded filter frame provided with a peripheral groove on one face which accepts an injection molded elastic piece which snap fits into the groove. The elastic piece is suitably attached, generally by injection molding, to the periphery of a flat filter medium. This approach generally is only suitable for use in holding a flat filter media taut along the peripheral edge of the rigid frame similar to a window screen. WO 96/29138 describes an injection molded filter frame piece which grips the edge of a filter medium by two snap fit side pieces which move toward each other and snap into a central rigid structural element. The snap fit pieces have projections that come together and hold the edges of the filter medium. Comer snap fit, frame pieces are separately provided to hold the filter media and frame to a rectangular form. The object of this invention was to provide a simple and cost effective method of manufacturing a filter frame, which can be recycled if need be. Generally, with all the above designs, the filter frame is created by forming individual frame elements that are three-dimensional in form. These three-dimensional frame elements must be directly attached to the filter media during formation of the frame or require further assembly that requires bringing together multiple three-dimensional elements.
Other patents have proposed forming a filter frame from a die cut flat material which is subsequently formed into a filter frame by folding the frame elements together into the final three-dimensional filter frame shape. For example, Japanese Publ. Patent Appln. 7-299317 describes a steel-type frame blank into which notches are cut to allow for tabs to be folded inward creating u-shaped channels. The notches allow the frame to be folded into a rectangular frame shape and subsequently welded together. Additional filter elements such as wire retaining elements can be provided on the opposite faces of the filter media. A much more complex shape is described in WO 94/11089 where the frame blank is described as punched from any suitable sheet material such as cardboard. Two separate sheets are cut which are mirror images of each other. Each sheet is symmetrical having three sections. One section is designed to hold and maintain the pleat form along a side of the pleated filter. The second section is designed to snap fit so as to hold the terminal end of the pleated filter. The third section engages the other sheet at a corner. The two folded sheets are then brought together with the two halves held together by slats and corresponding slits of the third section. A peripheral compressible sealing material is then provided along the external portion of the assembled frame to allow the frame to be friction fit into a housing. Although this frame allows a filter to be formed from a sheet of flat material, the complex three-dimensional folding along three separate axis makes this an inherently complicated assembly to manufacture in a continuous process not to mention the need for subsequent adhesive application of a sealing strip.
The present invention is directed at trying to provide a simple and convenient way to reinforce a framed pleated filter media.